Use direct members instead of pointers for viewableChunks and buyback

We had avoided putting STL containers into Players back when we thought
Players was still POD and needed to remain POD, but it turned out that
neither were the case all along, so there's no need for the indirection.

src/NPC.hpp

@@ -8,7 +8,7 @@ public:
     NPCClass npcClass;
     uint64_t instanceID;
     ChunkPos chunkPos;
-    std::set<Chunk*>* viewableChunks;
+    std::set<Chunk*> viewableChunks;
 
     int playersInView;
 
@@ -29,7 +29,6 @@ public:
         instanceID = iID;
 
         chunkPos = std::make_tuple(0, 0, 0);
-        viewableChunks = new std::set<Chunk*>();
         playersInView = 0;
     };
     BaseNPC(int x, int y, int z, int angle, uint64_t iID, int type, int id, NPCClass classType) : BaseNPC(x, y, z, angle, iID, type, id) {